Aircraft engine health is typically monitored using a Power Assurance Check (“PAC”). PACS generally measure and calculate engine horsepower as a function of measured gas temperature (“MGT”), corrected measured gas temperature (“MGTc”), or corrected gas generator speed (“NGc”) under steady operating conditions, before comparing that performance level to a baseline specification. The comparison to the baseline specification provides an indication of engine health level. PACs, however, have several limitations.
As one example, a PAC requires several minutes of stable, steady-state operation—i.e., in the case of a rotorcraft, several minutes of hover—in order to be performed accurately. To perform an automated PAC, a rotorcraft might have to hover for up to five minutes in relatively stable, wind-free conditions. If such conditions are not maintained for an adequate time period, the PAC routine will abort. Alternatively, a manual PAC can be performed. While a manually performed PAC will not abort because of a shorter period of stable, steady-state operation, accuracy will suffer if the period of steady operation is significantly shorter. Manually performed PACs also introduce human error in plotting performance data points, charting a line or curve on a graph, and interpreting the graph to predict available power and determine engine health. And manual performance of a PAC can be burdensome for a flight crew, or require additional personnel. For instance, for an aircraft requiring two pilots, one pilot must fly the aircraft while the other records the data and interprets the results. Alternatively, the flight crew could include a flight engineer to perform the PAC analysis, but the additional crew member diminishes the aircraft's capacity.
Another limitation of PACs is that it generally assumes that if, for example, an engine is providing 100% of baseline performance at one load level, it will provide 100% performance at higher loads as well. But engine health often differs at different engine load levels. As a result, for example, a PAC can indicate 100% engine health, only to have the pilots find that only 94% of the predicted power level is actually available when they reach higher altitude, attempt to lift heavier loads, or enter worse operating environments. Thus, the flight crew might find that the engine is marginal when its performance is most crucial.
Yet another limitation of PACs is that, for best accuracy, a PAC should be performed at high engine loads, e.g., within about 100° F. of the engine's maximum MGT rating. But reaching such a high engine load can require high altitudes, heavier aircraft loads, and/or high outside air temperatures. These can be difficult or impossible to acquire, depending on conditions.
Consequently, a need exists for an engine health assessment system and method that: (1) does not require several minutes of stable, steady-state operation; (2) does not place a significant burden on the flight crew; (3) accurately predicts engine health and performance levels at all operating loads and power levels, based on historical data reflecting the individual engine's unique performance “fingerprint”; and (4) does not require operation at high power levels and loads to obtain accuracy. These and other advantages of the present invention will become apparent to one skilled in the art.